By just about any measure, the movement to battle climate change has grown so large that the truths of Al Gore's decade-old movie now seem more mainstream than inconvenient.

In Paris in December, 195 nations agreed to reduce greenhouse gases. In the United States, 70 percent of Americans say that climate change is real. Pope Francis has joined the call for action. Hundreds of thousands of people have come together for climate marches in Paris and New York, and demonstrators recently held fossil-fuel protests on six continents.

"That's what I call momentum," Daniel R. Tishman, the chairman of the board of the Natural Resources Defense Council, said in its recent annual report. "This isn't just the wind at our backs; these are the winds of change."

But the movement that started with a straightforward mission — to get more people to appreciate the dangers of climate change as a precursor to action — is feeling growing pains. What may seem like a unified front has pronounced schisms, with conflicting opinions on many issues, including nuclear power and natural gas, that are complicating what it means to be an environmentalist in this day and age.

The factional boundaries are not hard and fast, with groups shifting their positions as the science and waves of activism evolve. The environmental movement has always been a congregation of many voices, and some disagreement should be expected on such complex and intractable problems as saving the planet. Still, the tensions remain strong.

Consider some of the biggest points of contention:

Nuclear power

There are sharp disagreements over whether nuclear plants should be part of the energy mix to reduce greenhouse gas emissions. Disasters like that at the Fukushima plant in Japan have undercut confidence in the technology, but it remains attractive to the Obama administration and many in the environmental movement, including James E. Hansen, a retired NASA climate scientist.

Supporters argue that nuclear plants can produce enormous amounts of power without the carbon dioxide that burning coal and natural gas produce. They also point out that the energy sources replacing existing plants tend to come from natural gas, causing greenhouse emissions. That was the case in New England when the Vermont Yankee plant was shut down, and in California after the closing of the plant at San Onofre.

Opponents of nuclear energy argue that the move to renewable energy sources would not require a new generation of nuclear plants. Naomi Oreskes, a Harvard historian who has written about the tactics of those who spread doubt about climate change, said proponents of nuclear power had not proved that the risks of operating the plants, and the waste they produce, could be managed.

"We all agree that there is urgency to this matter," she said in an email interview. "So do we really want to bet the planet (literally) on a technology with such a bad track record? And that even when it works takes decades to build?"

She has called the pronuclear arguments from environmentalists "a new, strange form of denial," pointedly using a word associated with those who have disputed the validity of climate science itself.

Natural gas

Burning natural gas produces less carbon dioxide and smog-producing pollutants than burning coal, so environmental groups such as the Sierra Club and even President Barack Obama once praised it as a "bridge" to renewable fuels: that natural gas plants could replace coal plants until alternate sources like solar and wind power could take over.

More recently, however, the environmental effects of hydraulic fracturing, or fracking, which is used to extract fossil fuels, and growing worries about the greenhouse gas methane, which often leaks when natural gas is produced and transported, have led many scientists and activists to call natural gas a "bridge to nowhere." (The Sierra Club now has a "Beyond Natural Gas" campaign.)

Climate campaigners like Bill McKibben have argued that the potency of methane as a greenhouse gas, especially in the short term, might make it worse than coal. He has described those who favor natural gas as a way to reduce greenhouse emissions as believers in "painless environmentalism, the equivalent of losing weight by cutting your hair."

The fight has made its way into the Democratic campaign for the presidency: Sen. Bernie Sanders of Vermont called for a national ban on fracking, while Hillary Clinton has suggested that the technology should be carefully regulated and that, if natural gas is a bridge to alternate energy sources, "we want to cross that bridge as quickly as possible." Those putting together the Democratic Party platform narrowly rejected the call for a ban.

Fossil-fuel companies

Two distinct camps have emerged on the best strategy for dealing with companies like Exxon Mobil. One camp wants to attack their very existence, and to hurt their businesses and reputations as a way of accelerating the transition to renewable technologies such as wind and solar.

Universities and institutional shareholders such as pensions and church endowments are being pressed to sell their stock in fossil-fuel companies, to fight projects like the Keystone XL pipeline and to disrupt construction of fossil-fuel facilities.

This approach animates the "keep it in the ground" campaign led by groups like McKibben's 350.org, which argues that many of today's fuel reserves are "unburnable" if climate change is to be slowed, and so must be considered "stranded assets" — a notion that oil giants like Exxon Mobil and Chevron reject.

On the other side is the camp that wants to engage with the companies, particularly through shareholder proxies, to push for action on climate change.

Groups like the Tri-State Coalition for Responsible Investment, as well as New York state and city officials, recently presented at Exxon Mobil's annual shareholder meeting proposals that would require the company to assess the business risks of meeting the Paris climate goals and to "acknowledge the moral imperative" to keep global temperatures from rising by more than 2 degrees Celsius (3.6 degrees Fahrenheit) since the start of the industrial era; they also helped to pass a resolution giving shareholders greater say in corporate governance.

Shareholder action has improved corporate responsibility on many fronts, said Sister Patricia Daly, a Dominican sister of Caldwell, New Jersey, who is the executive director of the Tri-State Coalition for Responsible Investment.

"Companies know the work we have put on their desk is beneficial," she said in a recent interview, and cited the emergence of sustainability directors and efforts by many companies to reduce their emissions. "I'm confident we have really initiated that over the decades," she said.

Insiders vs. outsiders

More fundamentally, a split is growing between the large, traditional environmental groups that try to work with companies and the scrappy campaigners who stand proudly outside.

Naomi Klein, an author on environmental and economic issues, has sharply criticized what she called "a very deep denialism in the environmental movement among the big green groups," like the Environmental Defense Fund, which has worked with fossil-fuel companies to research methane leaks and to pursue market-based solutions to the climate crisis, such as putting a price on carbon.

Klein argues that capitalism inherently worsens climate change. Working within the system as the institutional players do, she has said, is "more damaging than the right-wing denialism in terms of how much ground we've lost."

McKibben said the kind of noisy activism that characterizes the work of organizations like 350.org helps correct what he sees as the institutional inertia of the established groups. He said the lack of mass-movement activism was a key reason behind the failure of legislation such as the 2010 effort to develop a system to limit and put a price on greenhouse gas emissions.

"If we're going to win the climate fight, it will come with a change in the zeitgeist," he said. "And that — not particular pieces of legislation — is the ultimate point of building movements."

Fred Krupp, the president of the Environmental Defense Fund, disagreed. Working with industry, he said, had helped deepen the understanding of such issues as methane leakage, which could produce remedies.

"More and more businesses want to be part of the solution," Krupp said. Collaborative efforts helped lead to last month's bipartisan passage of an overhaul of toxic substances legislation, he said, adding, "And we're getting close to being able to do it with climate change."

Given these fault lines on various issues, a question naturally arises: Are they hurting the overall environmental movement?

Even on that question, there are disagreements.

For Matthew Nisbet, an expert in environmental communications at Northeastern University, there is a risk that differences of opinion within the movement could lead to greater enmity over time, resulting in a lack of focus. Progress could be lost, he said, "if they start to see each other as rivals and opponents, and they lose sight of broader climate goals and their true opponents."

But many in the various factions of the movement say that there is more agreement than it may seem from afar.

Krupp said that although tactics and technologies may differ, consensus has emerged on many points.

"We have to keep most of the fossil fuels in the ground," he said. "We all agree with that. The math dictates that. We all agree that the conversion to clean energy should be as quick as possible." Of natural gas, he said, "it's an exit ramp, not a bridge."

The movement to combat climate change is building an even bigger tent as more nations, businesses, religious groups and even conservatives have committed to dealing with the threat of rising seas and changing weather.

The number of Republicans speaking out in favor of climate action is growing, with the emergence of climate-oriented conservative groups such as R Street and the efforts of Jay Faison, a philanthropist who has pledged millions of dollars to support candidates willing to buck the party's orthodoxy on climate change.

Ellen Dorsey, the executive director of the Wallace Global Fund, which has promoted the divestment of fossil-fuel holdings and investment in cleaner technologies, has called disagreements within the green camp "noises around the margin." She predicted that a combination of high-level collaboration and street-level activism would hold governments to their Paris climate pledges and push back against recalcitrant business interests.

Ultimately, Gore said in a recent telephone interview, economics may accomplish much of what governments have so far failed to do. Plunging costs of renewable energy make it more competitive than ever with fossil fuels. Similarly, the former vice president said, the biggest obstacle for nuclear power could be the expense of building new reactors.

"I don't have a theological opposition to nuclear power," he said. "It's simply not cost competitive."

Gore said that tensions among climate change activists follow the traditions of the civil rights movement, abolition, women's suffrage and gay and lesbian rights. "In all such movements, there have been schisms, and minor splits as well," he added. "It's just a natural feature of the human condition."